A technique called “beamforming” has in recent years been widely known, which is used by a base station having a plurality of antenna elements to form a beam aimed at a terminal apparatus using the plurality of antenna elements. For example, Long Term Evolution (LTE) release 10 specifies that a base station is equipped with eight antennas.
According to beamforming, a beam aimed in a desired direction is formed by multiplying a signal of each antenna element by a weight coefficient. For example, according to LTE, a terminal apparatus selects a recommended one from sets of weight coefficients (i.e., precoding matrices) contained in a codebook, and notifies a base station of the recommended set of weight coefficients. Alternatively, a base station calculates a set of weight coefficients on the basis of a reference signal transmitted by a terminal apparatus.
For example, Patent Literature 1 describes a technique of using a combination of a first type of precoding weights and a second type of precoding weights.